Snare with loop made of heat shrinkable shape memory material and method of use thereof

ABSTRACT

A tissue snare comprises an elongated member having a distal end and a loop formed of a shape memory material, the loop including a tissue receiving interior opening and being connected to the distal end of the elongated member, properties of the shape memory material being selected so that, when a temperature of the loop exceeds a critical temperature thereof, the loop constricts from an expanded state to a constricted state. A method of treating tissue comprises placing a loop of a snare around a portion of tissue to be treated while the loop is in an expanded configuration, the loop being formed of a shape memory material having a critical temperature so that, when a temperature of the loop is above the critical temperature, the loop transitions from the expanded configuration to a constricted configuration in combination with transitioning, after the loop has been placed around the portion of tissue to be treated, the loop from the expanded configuration to the constricted configuration to tighten the loop around the portion of tissue to be treated.

BACKGROUND

Polyps are abnormal growths that typically extend from an inner wall ofa hollow organ and may be precursors to more serious ailments such ascancer. Polyps may develop in different parts of a patient's body, forexample the gastro intestinal (GI) tract, the uterus, the heart, etc.However, polyps which develop in the intestine, especially in the colonand the rectum, are serious as they are often a precursor for colorectalcancer. Thus, treatment of these polyps before they develop intomalignancies is extremely important.

Several procedures available for the removal of polyps generally areapplicable to colorectal polyps in particular. Snares are commonly usedto grip and remove polyps. In some instances, the polyp is notimmediately removed. Rather, the snare is tightened around the polyp andleft in place to act as a ligation band, choking the supply of blood tothe polyp so that it withers and dies over time.

Various types of snares are commonly used to remove polyps, for examplefrom the intestine wall. These snares all require a mechanism to tightena loop of the snare around the polyp so that it can be gripped andremoved from the underlying tissue layers. Generally, the tightening isdone mechanically, by providing a linkage between the loop and a controlhandle, so that the surgeon can manually tighten the loop. Levers,pulleys, cables or other devices may be used to facilitate thetightening of the loop around the polyp. However, the linkagesconnecting these loops to the controls and associated elements is oftenbulky, making the snare device too large to be inserted endoscopicallyand/or to be manipulated as necessary.

Polyps may also be removed through hot biopsy in which a forceps is usedto grip the polyp between jaws which are heated to ablate the base ofthe polyp so it can be retrieved and evaluated. Destructive techniquessuch as argon beam coagulation are also used to treat polyps. In theseprocedures, energy (e.g., laser energy) is directed to the polyp tonecrose the tissue.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a tissue snarecomprising an elongated member having a distal end and a loop formed ofa shape memory material, the loop including a tissue receiving interioropening and being connected to the distal end of the elongated member,properties of the shape memory material being selected so that, when atemperature of the loop exceeds a critical temperature thereof, the loopconstricts from an expanded state to a constricted state.

The present invention is further directed to a method of treating tissuecomprising placing a loop of a snare around a portion of tissue to betreated while the loop is in an expanded configuration, the loop beingformed of a shape memory material having a critical temperature so that,when a temperature of the loop is above the critical temperature, theloop transitions from the expanded configuration to a constrictedconfiguration in combination with transitioning, after the loop has beenplaced around the portion of tissue to be treated, the loop from theexpanded configuration to the constricted configuration to tighten theloop around the portion of tissue to be treated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a snare device to remove polyps according tothe present invention, in an open configuration;

FIG. 2 is a diagram showing the snare device of FIG. 1 in a tightenedconfiguration;

FIG. 3 is a diagram showing another embodiment of the snare deviceaccording to the invention;

FIG. 4 is a diagram showing a third embodiment of the snare deviceaccording to the invention; and

FIG. 5 is a diagram showing a further embodiment fo the snare deviceaccording to the invention.

DETAILED DESCRIPTION

The present invention may be further understood with reference to thefollowing description and the appended drawings, wherein like elementsare referred to with the same reference numerals. The present inventionrelates to devices for removing polyps from hollow organs and, inparticular, relates to a snare for removing intestinal polyps. Thepresent invention relates generally to the treatment of diseases andinjuries to tissue that respond to constriction of the tissue and may beused, for example, to treat bleeding by forming a constriction around aninjured portion of tissue.

Conventional treatments for polyps, particularly intestinal polyps,include hot biopsy, snaring and ablation. During ablation, energy issupplied to the polyp to disrupt cellular activity, For example, laserenergy may be directed to the polyp in the form of an argon beam orother laser beam, to cause coagulation and necrosis. RF or otherelectrical energy may be used to heat a device, a target portion oftissue or both. Ablation and other destructive techniques are often usedwhen colonoscopy or other endoscopic procedures for removing andcollecting the polyp cannot be performed (e.g., for reasons related tothe patient's health). Because these procedures destroy the tissue, theydo not allow for a biopsy of the polyp to determine, for example,whether the polyp is cancerous. Thus, these treatments are not asfavored as those which remove the tissue intact.

One common method of achieving this result is a hot biopsy procedure. Inthis procedure, a distal end of a forceps is placed in proximity to thepolyp and clamps of the forceps are placed around the base of the polyp.The clamps are then heated to cauterize and ablate the base of thepolyp, detaching the polyp from the surrounding tissue. The balance ofthe polyp is available substantially undamaged for collection andbiopsy. This procedure is often used to treat relatively small polyps,where the clamps of the forceps can be placed around the base of thepolyp with the heat serving to aid in hemostasis.

Snaring, which is also commonly used to remove polyps, involvespositioning a loop around the base of a polyp and tightening the wiretherearound so that the loop closes around the polyp, slicing it fromthe wall of the underlying organ. This procedure is commonly carried outto remove polyps in the bowels, so that they may be retrieved andbiopsied. With conventional snares, the loop is tightened through manualoperation of an actuator coupled to the snare by a mechanical linkage,for example, by squeezing a hand control or moving a lever coupled to acontrol wire which is attached to the snare. Polyps of various sizes maybe treated in this manner by employing snares of different dimensions.

However, the actuators and mechanical linkages used to tighten the loopincrease the size of these devices which may make them too large for usein certain endoscopic and other minimally invasive procedures.Particularly, snare devices are often inserted into the body throughendoscopes or colonoscopes. Additionally, since the devices are actuatedmanually, it may be difficult to maintain the snare in the properposition over the polyp while, at the same time, tightening the looparound the polyp. This issue is more serious when treating small polypsin difficult to reach places. Conventional snare devices tend to bestraight, with a long, relatively inflexible deployment cannula. Thusthese devices are unsuitable for polyps in certain, less accessiblelocations. In addition, such manually operated devices comprisemechanical components which may fail during use. Furthermore, assemblycomplexity and manufacturing costs are increased with the addition ofthese components.

A device according to the present invention includes a snare with a loopformed of a shape memory material. As would be understood by thoseskilled in the art, a variety of known metal alloys and polymers may bemanufactured with shape memory properties. Shape memory refers to theability of the material to “memorize” a shape, so that, after beingforced into another shape by strain, i.e. application of a forcethereto, they return to the originally memorized shape underpredetermined conditions. Generally, the change in condition whichbrings about a return to the original memorized condition is a change intemperature above or below a critical temperature. For example, a shapememory material may be formed into a wire having a certain length. Thewire may then be cooled below its critical temperature and subject to astrain to stretch the wire to a greater length, where it will remainuntil heated above the critical temperature. When the temperature of thewire exceeds the critical temperature, it will return to its originalshorter length.

Those skilled in the art will understand that several metallic alloyshave been developed which possess shape memory properties. For example,Nitinol which is an alloy containing nickel and titanium possesses shapememory properties that are well suited for application in medicalimplants. These alloys exist in one of two differenttemperature-dependent crystal structures which correspond to anaustenitic phase and a martensitic phase. At temperatures below acritical temperature, these alloys are martensitic. The martensite phaseof these alloys is soft and ductile and can be easily deformed byde-twinning the crystalline structure via an applied strain. Attemperatures above the critical temperature, the alloys are austenitic.Austenite is a strong and hard phase of these alloys, exhibitingproperties similar to those of titanium, and is characterized by a muchmore regular crystalline lattice structure. These alloys may alsoundergo a phase change as a result of the application of strain. Forexample, an element in the austenitic phase may be bent so that, at highstrain locations, the alloy becomes martensitic. If the alloy isdesigned to have an unstable martensite phase at a selected operatingtemperature, removal of the strain results in a reverse transformationthat straightens the bending. The strain may be removed, for example, byheating the alloy above the critical temperature.

Polymeric shape memory materials have properties similar to those of themetallic shape memory alloys, although those properties result fromdifferent physical effects and processes. As such, elements formed fromshape memory polymers may be given a base shape and then cooled belowthe critical temperature where a strain is applied to deform thepolymer. When the element is heated again to a temperature above thecritical temperature, it regains the shape that it had before the strainwas applied. Examples of polymers that have been utilized in hard andsoft phases of shape memory polymers include polyurethanes,polynorborenes, polyethers, polyacrylates, polyamides, polysiloxanes,polyether amides, polyether esters, trans-polyisoprenes,polymethylmethacylates, cross-linked trans-polyoctylenes, cross-linkedpolyethylenes, cross-linked polyisoprenes, cross-linkedpolycyclooctenes, inorganic-organic hybrid polymers, co-polymer blendswith polyethylene and Kraton, styrene-butadiene co-polymers,urethane-butadiene co-polymers, PMMA, polycaprolactone or oligocaprolactone co-polymers, PLLA or PL/D LA co-polymers, PLLA PGAco-polymers, and photocrosslinkable polymers including azo-dyes,zwitterionic, and other photochromatic materials such as those describedin “Shape Memory Materials” by Otsuka and Wayman, Cambridge UniversityPress 1998, the entire contents of which are incorporated herein byreference.

For example, a wire formed of a shape memory material may contract whenwarmed above the critical temperature causing the wire to shrink and, ifformed as a snare, contraction of the loop of the wire will cause thesnare to constrict. In an exemplary use of the device according to theinvention, a loop of a snare is inserted into the intestine in anexpanded configuration via, for example, a colonoscope or otherendoscopic instrument. The material of which the snare is formed ispreferably designed so that a critical temperature of the material is aselected amount above an ambient temperature in the environment in whichthe snare is to be deployed (e.g., body temperature) so that the timingof contraction of the snare may be controlled by selectively heating thesnare to the critical temperature when phase change is desired.Alternatively, a material with a critical temperature lower than bodytemperature may be selected so that the snare is deployed as it warmsabove the critical temperature.

The loop is positioned around a polyp while the wire is still in theexpanded configuration (i.e., before the wire is warmed to the criticaltemperature). Then, as the temperature of the loop approaches bodytemperature or is heated to the critical temperature, the shape memoryproperties of the wire are activated causing it to shrink and tightenaround the base of the polyp. Those skilled in the art will understandthat the snare may be designed to tighten until the polyp is cut offfrom the underlying tissue or until blood flow to the polyp is cut off.When tightened to the point of resection, the polyp will be left intactfor retrieval and biopsy while, in the case of the cut off of bloodflow, the polyp will slowly whither and slough off.

Pedunculated polyps may be treated directly with the exemplary loop, byplacing the loop around the polyp's stalk before heating. Polyps withoutstalks (e.g., flap and sessile polyps) may require an injection of afluid under their bases before they are elevated from the underlyingtissue sufficiently to be removed by the snare. Once such a polyp hasbeen elevated from the underlying tissue, the procedure is the same asdescribed above.

In an exemplary embodiment according to the invention, the heating iscarried out by controlling circulation of a hot fluid in a heat exchangearea in contact with the shape memory material. However, other methodsof heating the loop may be used as well. For example, the shape memorymaterial may be heated by an electric element placed adjacent to theloop, embedded within the loop, wrapped around the loop or as acomponent of the loop, such as a resistor extending proximate to theshape memory element. Other sources of heat located near the loop mayalso be used, such as active heat sources or conductive elements whichconvey heat to the shape memory element from a more remote source.Alternatively, an external source may heat the loop. For example,magnetic or electric fields may be used to heat the loop by induction toa temperature greater than the critical temperature, while using asource of energy external to the patient, or remote from the shapememory element. For example, a loop may be formed of a polymer withparticles responsive to the applied energy embedded therein.Alternatively, the loop may be heated using focused high frequencyultrasound as would be understood by those skilled in the art.

FIG. 1 shows an exemplary embodiment of a loop snare device according tothe invention. The snare device 100 comprises an elongated portion 102and a loop portion 104. The elongated portion 102 is designed to beinserted into a body, for example, through an endoscope to a target siteincluding a tissue growth (e.g., a polyp) to be removed. In oneembodiment, elongated portion 102 is sufficiently resilient so that itis able to support the loop portion 104 as the user positions itproximate to the polyp. The elongated portion 102 also retains a certainamount of flexibility to pass through curving passages of a flexibleendoscope extending through, for example, a curved body lumen. Theoverall dimensions of the snare device 100 are preferably compatiblewith use through the working channel of an endoscope or colonoscope. Forexample, a snare device 100 of 0.5-3.5 mm diameter may be suitable foruse with a colonoscope having a working channel of 2-4 mm diameter.

The loop element 104 is formed of the shape memory material as describedabove. In the exemplary embodiment, the shape memory material is apolymer which is maintained below its critical temperature duringinsertion into the body. To achieve this, the critical temperature maybe selected to be higher than body temperature as described above. Inthis condition as shown in FIG. 1, the loop 104 is expanded to theinsertion configuration, with a relatively large opening 108 definedthereby. The loop 104 is selected so that the opening 108, in theinsertion configuration, is larger than the polyp to be treated allowingthe user to maneuver the elongated portion 102 and the loop 104 over thepolyp and around the base thereof. The specific shape of the loop 104may be varied depending on the procedure being carried out. For example,the loop 104 may be circular, oval or any other conventional shape usedin the construction of snare devices. The dimensions of the loop 104 maypreferably selected to fit the size of the polyp, being treated and,thus, will vary from case to case. In addition, the snare may be shapedto include a sharp inner surface or tissue cutting blade.

FIG. 2 shows the snare device 100 in the constricted configuration afterthe loop 104 has been reduced in size to that of the loop 104′. The loop104 returns to the constricted configuration 104′ shown in FIG. 2 afterundergoing a reverse transformation. In the case of the exemplary shapememory polymer, the transformation takes place due to heating above acritical temperature. In the embodiment shown in FIGS. 1 and 2, the loop104, 104′ is heated by placing a heated fluid in contact therewith. Asshown, a conduit 106 extends through the elongated portion 102, from aproximal source of heated water (not shown) to the loop 104, 104′.Within the loop 104, 104′, a second conduit 110 may form a leak-proofpath to deliver heated water to the interior of the loop 104, 104′thereby preventing hot fluid from injuring surrounding tissue. Inaddition, the conduits 106, 110 may provide either a one way or arecirculating flow path. The latter may be carried out by providing adual lumen conduit 106 and means to move the fluid through loop 104,such as a pump or recirculator as would be understood by those skilledin the art.

FIG. 3 shows a different embodiment of a snare device according to thepresent invention. In this embodiment, the snare device 200 comprises anelongated shaft 202 and a loop portion 204 formed of a shape memorymaterial, for example, a shape memory polymer or alloy which returns toan original, reduced dimension configuration as a result of heatingabove a critical temperature. A conduit 206, extending along or withinthe elongated shaft 202 to the loop element 204, conveys heated fluidthereto from a fluid source and terminates in a manifold 210 having aplurality of flow dispensing elements such as nozzles 212, directedtowards the loop 204. According to this exemplary embodiment, the heatedfluid does not circulate within the loop 204, but rather is providedexternally on the shape memory material to cause the contraction of theloop 204.

As compared with loop designs including an internal heated fluidconduit, externalizing the flow of heated fluid around the loop 204 asdescribed above simplifies construction and reduces the cost anddifficulty associated with manufacture of the device. However, as theunconstrained heated fluid may damage surrounding tissue, the device maynot be suitable for all applications and shielding may be necessary toprotect the surrounding tissue from the heated fluid. The heated fluidmay include therapeutic compounds to aid in treating the target tissueor, alternatively, may include components which, when mixed generateheat through an exothermic reaction to raise the temperature of thesnare over the critical temperature.

Those of skill in the art will understand that additional methods ofheating the shape memory elements may be used in the various embodimentsof the present invention. As described, a heated fluid may be used,either in a fully contained system as in the embodiment shown in FIGS.1, 2, or in a system where the fluid is allowed to escape, as in theembodiment of FIG. 3. In addition, the shape memory elements may beheated using different physical principles. For example, electricheating elements may be used to bring about the change in state of theshape memory elements from an expanded configuration to a contractedconfiguration. Heating of the shape memory material may also be obtainedby magnetic or electric induction. For example, a magnetic shape memorymaterial may be heated by generating a magnetic field outside thepatient's body, in proximity to the shape memory element.

FIG. 4 shows a snare device 300 having an elongated shaft 302 connectedto a loop portion 304 formed of a shape memory material. An electricconnection 306 is provided between a source of electric power (notshown) which, for example, remains outside the body and a heatingelement 308 in contact with the loop 304. As would be understood bythose skilled in the art, the pattern, extent and size of the heatingelement 308 may be varied to achieve specific amounts and rates ofchange of various portions of the loop 304 to, for example, control theshape of the loop 304 during and/or after constriction and/or to controlthe speed of constriction. If the loop 304 is formed of a shape memorymetal alloy which conducts electricity, a separate heating element maybe unnecessary as the loop 304 may receive current from the power sourceand serve as the heating element 308.

As described above, the amount of constriction of the loop elementaccording to the present invention depends upon a composition of theshape memory material and an amount of heating provided, among otherfactors. As described above, a loop snare may be constructed so that theamount of constriction, although insufficient to completely sever thepolyp from the underlying tissue, ligates the polyp to cut-off bloodsupply thereto. Those skilled in the art will understand that an amountof constriction sufficient to sever polyps of a given size, may beobtained by altering the design of the shape memory elements.

For example, FIG. 5 shows a curved shape memory element 402 extendingfrom a shaft 408 of a snare device 400. By selecting an appropriateshape of the shape memory element 402, a mechanical advantage is gainedwhich, when employed with a properly constituted shape memory materialallows the snare device 400 to directly remove the targeted polyp fromthe underlying tissue. Specifically, the device 400 includes asubstantially straight cord member 404 which couples a distal end of thecurved shape memory element 402 to the distal end of the shaft 408. Thecord member 404 is preferably composed of the same shape memory materialas the shape memory element 402 so that, when heated, the cord member408 contracts linearly as the shape memory element 402 constricts aroundthe polyp. Linear contraction of the cord member 404 draws the distalend of the shape memory element 402 toward the distal end of the shaft408 so that, when combined with the annular constriction of the shapememory element 402, opposed sides of the snare loop are drawn tautadjacent one another along a substantially straight line.

In yet another embodiment according to the present invention, the shapememory material is formed so that its critical temperature is below theaverage temperature of the human body. In this embodiment, the shapememory material is designed to remain in the stressed configuration atroom temperature, and to return to the original configuration as itexceeds the critical temperature while approaching the ambienttemperature within the body. For example, the loop of the snare may bemade of a shape memory material which retains an open, enlargedconfiguration when cooled to a temperature lower than its criticaltemperature which is, in turn, lower than body temperature. Wheninserted into the body, the loop warms until its temperature exceeds thecritical temperature and then constricts to the original, smaller size.As a result, the snare tightens to act as a ligating band or cuttingsnare as described above.

If it is desired to maintain the shape memory material below thecritical temperature so that the shape memory element retains thestressed shape until the snare is properly positioned, for example,around a polyp, a cooling fluid may be supplied to counteract thewarming effects of the body heat. For example, a conduit such as thatdescribed with reference to FIGS. 1 and 2 may be used to supply coolingfluid instead of a heating fluid. Then, when the snare has reached thedesired location and has been placed around a target portion of tissue(e.g., a polyp), the cooling flow is stopped and the body heat raisesthe temperature of the shape memory element above the criticaltemperature and constricts the snare. Those skilled in the art willunderstand that the snare may be made detachable from the applicator sothat it may be left in place around the target tissue, functioning likea ligating band.

The present invention has been described with reference to specificexemplary embodiments. Those skilled in the art will understand thatchanges may be made in details, particularly in matters of shape, size,material and arrangement of parts. Accordingly, various modificationsand changes may be made to the embodiments. Additional or fewercomponents may be used, depending on the condition that is being treatedusing the snare device. The specifications and drawings are, therefore,to be regarded in an illustrative rather than a restrictive sense.

1. A tissue snare comprising: an elongated member having a distal end;and a loop comprising a shape memory material, the loop including atissue receiving interior opening and being connected to the distal endof the elongated member, properties of the shape memory material beingselected so that, when a temperature of the loop exceeds a criticaltemperature thereof, the loop constricts from an expanded state to aconstricted state.
 2. The snare according to claim 1, wherein the shapememory material is a shape memory polymer.
 3. The snare according toclaim 1, wherein the shape memory material is a shape memory metal. 4.The snare according to claim 1, further comprising a temperature controlapparatus controlling a temperature of the loop to control transitionsof the loop between the expanded state and the constricted state.
 5. Thesnare according to claim 4, wherein the temperature control mechanismincludes a fluid lumen extending to the distal end of the elongatedmember to provide one of cooling and heating fluid to the loop.
 6. Thesnare according to claim 5, wherein the temperature control mechanismfurther comprises a fluid conduit extending along at least a portion ofthe length of the loop.
 7. The snare according to claim 6, wherein thefluid conduit extends from a distal opening of the fluid lumen, withinthe loop.
 8. The snare according to claim 5, further comprising a fluiddispensing opening located adjacent to the distal end of the elongatedmember for directing fluid from the fluid lumen, toward an exteriorsurface of the loop.
 9. The snare according to claim 4, wherein thetemperature control mechanism further comprises a heating elementpositioned along at least a portion of the length of the loop.
 10. Thesnare according to claim 3, wherein the heating element is integrallyformed with the loop.
 11. The snare according to claim 2, wherein theheating element is bonded to an exterior surface of the loop.
 12. Thesnare according to claim 1, wherein the shape memory material isselected so that the critical temperature is greater than an ambienttemperature to which the distal end will be exposed when in an operativeposition.
 13. The snare according to claim 1, wherein the loop includesa first section extending along a curve from a distal end of theelongated member to a first section distal end separated from the distalend of the elongated member and a second section extending along asubstantially straight line between the distal end of the elongatedmember and the first section distal end.
 14. A method of treating tissuecomprising: placing a loop of a snare around a portion of tissue to betreated while the loop is in an expanded configuration, the loop beingformed of a shape memory material having a critical temperature so that,when a temperature of the loop is above the critical temperature, theloop transitions from the expanded configuration to a constrictedconfiguration; and after the loop has been placed around the portion oftissue to be treated, transitioning the loop from the expandedconfiguration to the constricted configuration to tighten the looparound the portion of tissue to be treated.
 15. The method according toclaim 14, wherein the loop is transitioned from the expandedconfiguration to the constricted configuration by applying heat to theloop to raise the temperature thereof above the critical temperature.16. The method according to claim 14, wherein the critical temperatureis selected to be lower than an ambient temperature in an environment inwhich the loop is to be used and wherein the loop is transitioned fromthe expanded configuration to the constricted configuration by exposureto body heat.
 17. The method according to claim 16, wherein the loop ismaintained in the expanded configuration until a desired transition timeby cooling the loop to maintain a temperature thereof below the criticaltemperature.
 18. The method according to claim 17, wherein the loop isconnected to a proximal control handle via an elongated member andwherein heat is applied to the loop by supplying a heated fluid to theloop via a fluid conduit extending along the elongated member.
 19. Themethod according to claim 18, wherein the loop includes a fluid lumenextending therethrough, the fluid lumen receiving heated fluid from thefluid conduit.
 20. The method according to claim 15, wherein the loop isheated by an electric heating element.
 21. (canceled)
 22. (canceled)